CCNP實戰教程之 OSPF虛鏈路研究

課題內容：OSPF虛鏈路研究

實驗拓撲：

基本IP地址規劃：

R3-R5之間使用 10.1.35.0/30 子網

R一、R三、R4之間使用 10.1.1.0/24子網

R一、R二、R4之間使用 10.1.124.0/24子網

每臺設備的環回接口使用 10.1.6.X/32 X = 設備編號

幀中繼配置：

R2：

default int s1/0

default int s1/1

default int s1/2

frame-relay switching

interface Serial1/0

no ip address

no shut

encapsulation frame-relay

frame-relay intf-type dce

frame-relay route 103 interface Serial1/2 301

!

interface Serial1/1

no ip address

no shut

encapsulation frame-relay

frame-relay intf-type dce

frame-relay route 403 interface Serial1/2 304

!

interface Serial1/2

no ip address

no shut

encapsulation frame-relay

frame-relay intf-type dce

frame-relay route 301 interface Serial1/0 103

frame-relay route 304 interface Serial1/1 403

R1:

interface Serial1/0

no shutdown

ip address 10.1.1.1 255.255.255.0

encapsulation frame-relay

R3：

interface Serial1/2

no shutdown

ip address 10.1.1.3 255.255.255.0

encapsulation frame-relay

R4：

interface Serial1/1

no shutdown

ip address 10.1.1.4 255.255.255.0

encapsulation frame-relay

按圖所示配置OSPF

R1(config)#int lo0

R1(config-if)#ip ospf 1 area 0

R1(config-if)#int s1/0

R1(config-if)#ip ospf 1 area 100

R1(config-if)#int e0/1

R1(config-if)#ip ospf 1 area 2

R1(config-if)#router ospf 1

R1(config-router)#area 2 stub no-summary

R2(config)#router ospf 1

R2(config-router)#net

R2(config-router)#network 10.0.0.0 0.255.255.255 area 2

R2(config-router)#area 2 stub

R4(config)#int s1/1

R4(config-if)#ip os 1 a 100

R4(config-if)#int l0

R4(config-if)#ip os 1 a 100

R4(config-if)#int e0/3

R4(config-if)#ip os 1 a 2

R4(config-if)#router ospf 1

R4(config-router)#area 2 stub no-summary

R3(config)#int s1/2

R3(config-if)#ip ospf 1 area 100

R3(config-if)#int e0/3

R3(config-if)#ip ospf 1 area 1

R3(config-if)#int loopback 0

R3(config-if)#ip ospf 1 area 100

R3(config-if)#end

R5(config)#int loopback 0

R5(config-if)#ip ospf 1 area 1

R5(config-if)#int e0/3

R5(config-if)#ip ospf 1 area 1

R1(config-if)#ip ospf network point-to-multipoint

R3(config-if)#ip ospf network point-to-multipoint

R4(config-if)#ip ospf network point-to-multipoint

驗證：

R1#show ip ospf neighbor

Neighbor ID Pri State Dead Time Address Interface

10.1.6.2 1 FULL/BDR 00:00:35 10.1.124.2 Ethernet0/1

10.1.6.4 1 FULL/DROTHER 00:00:38 10.1.124.4 Ethernet0/1

10.1.5.3 0 FULL/ - 00:01:48 10.1.1.3 Serial1/0

R1#show ip ospf interface brief

Interface PID Area IP Address/Mask Cost State Nbrs F/C

Lo0 1 0 10.1.6.1/32 1 LOOP 0/0

Et0/1 1 2 10.1.124.1/24 10 DR 2/2

Se1/0 1 100 10.1.1.1/24 64 P2MP 1/1

R2#show ip ospf neighbor

Neighbor ID Pri State Dead Time Address Interface

10.1.6.1 1 FULL/DR 00:00:39 10.1.124.1 Ethernet0/2

10.1.6.4 1 FULL/DROTHER 00:00:35 10.1.124.4 Ethernet0/2

R2#show ip ospf interface brief

Interface PID Area IP Address/Mask Cost State Nbrs F/C

Lo0 1 2 10.1.6.2/32 1 LOOP 0/0

Et0/2 1 2 10.1.124.2/24 10 BDR 2/2

R3#show ip ospf neighbor

Neighbor ID Pri State Dead Time Address Interface

10.1.6.5 1 FULL/BDR 00:00:30 10.1.35.2 Ethernet0/3

10.1.6.1 0 FULL/ - 00:01:49 10.1.1.1 Serial1/2

10.1.6.4 0 FULL/ - 00:01:58 10.1.1.4 Serial1/2

R3#show ip ospf interface brief

Interface PID Area IP Address/Mask Cost State Nbrs F/C

Et0/3 1 1 10.1.35.1/30 10 DR 1/1

Lo0 1 100 10.1.5.3/32 1 LOOP 0/0

Se1/2 1 100 10.1.1.3/24 64 P2MP 2/2

R4#show ip ospf neighbor

Neighbor ID Pri State Dead Time Address Interface

10.1.6.1 1 FULL/DR 00:00:35 10.1.124.1 Ethernet0/3

10.1.6.2 1 FULL/BDR 00:00:38 10.1.124.2 Ethernet0/3

10.1.5.3 0 FULL/ - 00:01:55 10.1.1.3 Serial1/1

R4#show ip ospf interface brief

Interface PID Area IP Address/Mask Cost State Nbrs F/C

Et0/3 1 2 10.1.124.4/24 10 DROTH 2/2

Lo0 1 100 10.1.6.4/32 1 LOOP 0/0

Se1/1 1 100 10.1.1.4/24 64 P2MP 1/1

R5#show ip ospf neighbor

Neighbor ID Pri State Dead Time Address Interface

10.1.5.3 1 FULL/DR 00:00:31 10.1.35.1 Ethernet0/3

R5#show ip ospf interface brief

Interface PID Area IP Address/Mask Cost State Nbrs F/C

Lo0 1 1 10.1.6.5/32 1 LOOP 0/0

Et0/3 1 1 10.1.35.2/30 10 BDR 1/1

檢查路由：

R2#show ip route ospf | begin Gateway

Gateway of last resort is 10.1.124.1 to network 0.0.0.0

O*IA 0.0.0.0/0 [110/11] via 10.1.124.1, 00:13:47, Ethernet0/2

// 位於徹底末節區域的R2，僅僅收到了一條O IA的默認路由，那麼，這是不是正常現象？ //

R2#show ip ospf border-routers

OSPF Router with ID (10.1.6.2) (Process ID 1)

Base Topology (MTID 0)

Internal Router Routing Table

Codes: i - Intra-area route, I - Inter-area route

i 10.1.6.1 [10] via 10.1.124.1, Ethernet0/2, ABR, Area 2, SPF 3

注意: ABR的定義，必須至少有一個接口位於骨幹區域，一個接口位於非骨幹區域，這樣的OSPF路由器才被稱爲ABR；

R4#show ip route ospf | begin Gateway

Gateway of last resort is 10.1.124.1 to network 0.0.0.0

O*IA 0.0.0.0/0 [110/11] via 10.1.124.1, 00:20:19, Ethernet0/3

10.0.0.0/8 is variably subnetted, 10 subnets, 2 masks

O 10.1.1.1/32 [110/128] via 10.1.1.3, 00:13:48, Serial1/1

O 10.1.1.3/32 [110/64] via 10.1.1.3, 00:13:48, Serial1/1

O 10.1.5.3/32 [110/65] via 10.1.1.3, 00:13:48, Serial1/1

O IA 10.1.6.1/32 [110/129] via 10.1.1.3, 00:13:48, Serial1/1

O 10.1.6.2/32 [110/11] via 10.1.124.2, 00:20:19, Ethernet0/3

// R4沒有收到 區域1的路由 //

緣由是？ 普通區域之間是不能直接傳遞路由的；

區域之間的路由傳遞，本質上是由ABR對LSA進行生成或從新生成的過程；

R3並非ABR，所以沒法在區域 1 和區域 100之間轉換LSA；

R5#show ip route ospf | begin Gateway

Gateway of last resort is not set

// R5上一條OSPF路由都沒收到 //

那麼，觀察鏈路狀態數據庫，查找緣由；

R5#show ip ospf database

OSPF Router with ID (10.1.6.5) (Process ID 1)

Router Link States (Area 1)

Link ID ADV Router Age Seq# Checksum Link count

10.1.5.3 10.1.5.3 1269 0x80000002 0x00F6AD 1

10.1.6.5 10.1.6.5 1267 0x80000004 0x00EB88 2

Net Link States (Area 1)

Link ID ADV Router Age Seq# Checksum

10.1.35.1 10.1.5.3 1269 0x80000001 0x00834E

//R5的鏈路狀態數據庫中，僅僅存在Area 1的一類和二類LSA，沒有來自ABR的用於計算區域間路由的三類LSA以及其它類型的LSA； //

R5#show ip ospf border-routers

OSPF Router with ID (10.1.6.5) (Process ID 1)

Base Topology (MTID 0)

Internal Router Routing Table

Codes: i - Intra-area route, I - Inter-area route //從R5上查看，本區域並不存在ABR //

在一些特殊場景或者歷史遺留問題形成的特殊場景環境中，會形成OSPF區域規劃不合理的現象，這也將給路由的傳遞和優化帶來困難；

舉例一：

例如本圖中的 area 1，沒有與骨幹區域相鄰  （非骨幹區域遠離骨幹區域）

會形成沒法與相鄰區域交互路由信息；

舉例二：

如圖所示，骨幹區域因爲歷史緣由並不連續，將會形成以下問題：

按圖部署四臺路由器，OSPF的鄰居和鄰接沒有問題，接口宣告也沒有問題；

R1#show ip os neighbor

Neighbor ID Pri State Dead Time Address Interface

22.1.1.1 1 FULL/DR 00:00:34 12.1.1.2 Ethernet0/1

R1#show ip os int br

Interface PID Area IP Address/Mask Cost State Nbrs F/C

Lo0 110 0 11.1.1.1/32 1 LOOP 0/0

Et0/1 110 0 12.1.1.1/24 10 BDR 1/1

R2#show ip os neighbor

Neighbor ID Pri State Dead Time Address Interface

11.1.1.1 1 FULL/BDR 00:00:31 12.1.1.1 Ethernet0/1

33.1.1.1 1 FULL/DR 00:00:35 23.1.1.3 Ethernet0/2

R2#show ip os int br

Interface PID Area IP Address/Mask Cost State Nbrs F/C

Lo0 110 0 22.1.1.1/32 1 LOOP 0/0

Et0/1 110 0 12.1.1.2/24 10 DR 1/1

Et0/2 110 1 23.1.1.2/24 10 BDR 1/1

R3#show ip os neighbor

Neighbor ID Pri State Dead Time Address Interface

44.1.1.1 1 FULL/DR 00:00:39 34.1.1.4 Ethernet0/3

22.1.1.1 1 FULL/BDR 00:00:38 23.1.1.2 Ethernet0/2

R3#

R3#show ip os int br

Interface PID Area IP Address/Mask Cost State Nbrs F/C

Lo0 110 0 33.1.1.1/32 1 LOOP 0/0

Et0/3 110 0 34.1.1.3/24 10 BDR 1/1

Et0/2 110 1 23.1.1.3/24 10 DR 1/1

R4#show ip os neighbor

Neighbor ID Pri State Dead Time Address Interface

33.1.1.1 1 FULL/BDR 00:00:35 34.1.1.3 Ethernet0/3

R4#show ip os int br

Interface PID Area IP Address/Mask Cost State Nbrs F/C

Lo0 110 0 44.1.1.1/32 1 LOOP 0/0

Et0/3 110 0 34.1.1.4/24 10 DR 1/1

查看路由：

R4#show ip route ospf | begin Gateway

Gateway of last resort is not set

23.0.0.0/24 is subnetted, 1 subnets

O IA 23.1.1.0 [110/20] via 34.1.1.3, 00:01:41, Ethernet0/3

33.0.0.0/32 is subnetted, 1 subnets

O 33.1.1.1 [110/11] via 34.1.1.3, 00:01:41, Ethernet0/3

//R4的路由表中，並無左側一個區域0的路由；//

檢查LSDB，看是否有 LSA

OSPF ABR的水平分割規則： 從骨幹區域傳遞到非骨幹區域的三類LSA，不容許傳遞迴骨幹區域；

//也就意味着，舉例二中這個場景，將會形成兩個不連續的骨幹區域之間沒法交互路由 //

OSPF的虛鏈路主要用於解決以上兩種場景。

在場景二種部署虛鏈路：

由area 1 承載虛鏈路；

Note ： 規則：承載虛鏈路的區域必須是非特殊區域；

虛鏈路是屬於骨幹區域的一條鏈路；

配置：

在ABR上配置

R2(config-router)#area 1 virtual-link 33.1.1.1

R3(config-router)#area 1 virtual-link 22.1.1.1

// 注意，此處配置的對等體爲對端的 router-id //

R3#

*Sep 5 12:17:18.983: %OSPF-5-ADJCHG: Process 110, Nbr 22.1.1.1 on OSPF_VL0 from LOADING to FULL, Loading Done

// 日誌信息表示經過OSPF虛鏈路創建了一個徹底鄰接關係 //

R3#show ip ospf interface brief

Interface PID Area IP Address/Mask Cost State Nbrs F/C

VL0 110 0 23.1.1.3/24 10 P2P 1/1

R3#show ip ospf neighbor

Neighbor ID Pri State Dead Time Address Interface

22.1.1.1 0 FULL/ - - 23.1.1.2 OSPF_VL0

經過檢查命令，發現設備上多了一個虛鏈路的接口，以及一個虛鏈路的鄰居；

值得注意的是，虛鏈路在部署時，若是不加參數，默認將不記老化時間；

R3#show ip ospf interface

OSPF_VL0 is up, line protocol is up

Internet Address 23.1.1.3/24, Area 0, Attached via Not Attached

Process ID 110, Router ID 33.1.1.1, Network Type VIRTUAL_LINK, Cost: 10

Topology-MTID Cost Disabled Shutdown Topology Name

0 10 no no Base

Configured as demand circuit

Run as demand circuit

DoNotAge LSA allowed

Transmit Delay is 1 sec, State POINT_TO_POINT

Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5

oob-resync timeout 40

Hello due in 00:00:02

Supports Link-local Signaling (LLS)

Cisco NSF helper support enabled

IETF NSF helper support enabled

Index 3/4, flood queue length 0

Next 0x0(0)/0x0(0)

Last flood scan length is 1, maximum is 1

Last flood scan time is 0 msec, maximum is 0 msec

Neighbor Count is 1, Adjacent neighbor count is 1

Adjacent with neighbor 22.1.1.1 (Hello suppressed)

Suppress hello for 1 neighbor(s)

// 經過虛鏈路創建的鄰居，抑制hello報文，虛鏈路使用跟按需電路同樣的工做方法 //

R3#show ip ospf database

OSPF Router with ID (33.1.1.1) (Process ID 110)

Router Link States (Area 0)

Link ID ADV Router Age Seq# Checksum Link count

11.1.1.1 11.1.1.1 1013 (DNA) 0x80000003 0x00527B 2

22.1.1.1 22.1.1.1 1 (DNA) 0x80000005 0x007AD3 3

33.1.1.1 33.1.1.1 430 0x80000005 0x0036D1 3

44.1.1.1 44.1.1.1 1351 0x80000003 0x007BBD 2

// 經過虛鏈路學習到的 LSA，不記老化時間 //

虛鏈路規則（補）：

虛鏈路的一個端點必須在骨幹區域上；

首先想清楚，部署虛鏈路的目的是？

咱們要解決area 1 和area 100 沒有ABR的問題，所以，經過在 area 100 部署一條虛鏈路，將R3鏈接到 骨幹區域，使得R3成爲 ABR；

配置：

R1(config)#router ospf 1

R1(config-router)#area 100 virtual-link 10.1.6.3

R3(config)#router ospf 1

R3(config-router)#area 100 virtual-link 10.1.6.1

驗證：

R3#show ip ospf neighbor

Neighbor ID Pri State Dead Time Address Interface

10.1.6.1 0 FULL/ - - 10.1.1.1 OSPF_VL0

R5#show ip route ospf | begin Gateway

Gateway of last resort is not set

10.0.0.0/8 is variably subnetted, 11 subnets, 3 masks

O IA 10.1.1.1/32 [110/74] via 10.1.35.1, 00:02:00, Ethernet0/3

O IA 10.1.1.3/32 [110/10] via 10.1.35.1, 00:02:00, Ethernet0/3

O IA 10.1.1.4/32 [110/74] via 10.1.35.1, 00:02:00, Ethernet0/3

O IA 10.1.6.1/32 [110/75] via 10.1.35.1, 00:02:00, Ethernet0/3

O IA 10.1.6.2/32 [110/85] via 10.1.35.1, 00:02:00, Ethernet0/3

O IA 10.1.6.3/32 [110/11] via 10.1.35.1, 00:02:00, Ethernet0/3

O IA 10.1.6.4/32 [110/75] via 10.1.35.1, 00:02:00, Ethernet0/3

O IA 10.1.124.0/24 [110/84] via 10.1.35.1, 00:02:00, Ethernet0/3

// R5上已經可以收取到全部的OSPF路由了 //

可是，R3上去往 area 2的路由，沒有負載均衡，由於 R4並非ABR；

嘗試部署另外一條虛鏈路，使得R4也成爲ABR

在R1和R4之間部署虛鏈路：

R1(config)#router ospf 1

R1(config-router)#area 100 virtual-link 10.1.6.4

R4(config)#router ospf 1

R4(config-router)#area 100 virtual-link 10.1.6.1

R4#

*Sep 5 12:58:45.058: %OSPF-5-ADJCHG: Process 1, Nbr 10.1.6.1 on OSPF_VL0 from LOADING to FULL, Loading Done // 日誌顯示鄰接成功創建 //

驗證：

R3#show ip route ospf | begin Gateway

Gateway of last resort is not set

10.0.0.0/8 is variably subnetted, 12 subnets, 3 masks

O 10.1.1.1/32 [110/64] via 10.1.1.1, 00:07:30, Serial1/2

O 10.1.1.4/32 [110/64] via 10.1.1.4, 00:07:30, Serial1/2

O 10.1.6.1/32 [110/65] via 10.1.1.1, 00:07:20, Serial1/2

O IA 10.1.6.2/32 [110/75] via 10.1.1.4, 00:01:08, Serial1/2

[110/75] via 10.1.1.1, 00:07:20, Serial1/2

O 10.1.6.4/32 [110/65] via 10.1.1.4, 00:07:30, Serial1/2

O 10.1.6.5/32 [110/11] via 10.1.35.2, 00:06:47, Ethernet0/3

O IA 10.1.124.0/24 [110/74] via 10.1.1.4, 00:01:08, Serial1/2

[110/74] via 10.1.1.1, 00:07:20, Serial1/2

// 成功實現了路由的負載均衡 //

OSPF虛鏈路實用場景總結：

1，backbone區域被分割

2，非骨幹區域與骨幹區域不相鄰

3, 骨幹區域不可靠鏈路備份